1. Field of the Invention
The invention relates to a navigation apparatus for a vehicle which determines a route to a destination, and which provides route guidance while the vehicle travels.
The invention also relates to a navigation apparatus for a vehicle which determines the shortest route from a start point to a destination, and to a method of displaying intersections which promotes smooth traveling in the vicinity of the intersections.
2. Description of Related Art
Conventionally, there has been proposed a navigation apparatus which determines a route to a destination from either a start point or the present position of a vehicle, and which guides the vehicle to the destination in accordance with the determined route (see Japanese Patent Application Laid-open (kokai) No. 2-75909).
Also, there has been proposed an improved navigation apparatus in which there is designated at least one enroute point between a start point and a destination, and in which route-determination is performed while taking the enroute point(s) into consideration. For example, when points A and B between a start point and a destination are designated as enroute points, a route between the start point and the enroute point A, a route between the enroute points A and B, and a route between the enroute point B and the destination are determined. As a result, the user is provided with a single continuous route which starts from the start point and reaches the destination via the enroute points A and B (see Japanese Patent Application Laid-open (kokai) No. 23899).
However, the possibility exists that the user is not satisfied with a route which is provided by the system based on the enroute points designated in the above-described manner. To overcome this drawback, there has been proposed a technique as disclosed in Japanese Patent Application Laid-open (kokai) No. 5-165407. In this technique, if the user is not satisfied with a route which is provided by the system based on costs of the routes, there is performed a processing for increasing the apparent segment cost of the system chosen route and then determining a route which has the smallest segment cost so as to provide a route different from the previously determined route.
However, even when the route different from the previously determined route is calculated, it is not necessarily possible to obtain a route which satisfies the user with only one recalculation. Also, since the recalculation is performed for the entire route from the start point to the destination, a prolonged period of time is required to complete the route determination. In the above-described case, even when the user is satisfied with the entire route except for the route between the enroute points A and B, for example, the system changes the entire route including the route between the start point to the enroute point A and the route between the enroute point B and the destination with which the user is satisfied. This occurs because the system performs route determining processing after increasing the apparent segment cost of the previously determined route. Accordingly, it is impossible to provide a route with which the user is satisfied. This is especially true in an initial route determination in which the entire route from a starting point to a destination is determined, the calculation time increases as the distance to the destination increases. This, obviously, is not a preferable characteristic of a navigation system.
Also, there has been known a method of guiding a vehicle at each intersection, according to which an enlarged map of the vicinity of each intersection is stored in the form of graphic data, and the enlarged map of the vicinity of the intersection is displayed together with an arrow.
Moreover, various kinds of navigation apparatuses for vehicles have recently been proposed (e.g., Japanese Patent Application Laid-Open (kokai) Nos. 1-173298 and 2-75909).
However, the intersection displays provided by these navigation apparatuses are not satisfactory, because their displays are not changed in fine increments as the vehicle proceeds.